Semiconductor device having ball-bonded pads

ABSTRACT

A method for forming a semiconductor device comprises the steps of providing a semiconductor die having a plurality of pads thereon with at least one bond wire electrically coupled with one of the pads and providing a holder having a cavity therein. The die is placed in the cavity, then a layer of encapsulation is formed within the cavity to cover the die. Subsequently, the encapsulated die is removed from the cavity.

PRIORITY INFORMATION

This is a continuation of application Ser. No. 08/611,314 filed Mar. 5,1996 and issued Oct. 20, 1998 as U.S. Pat. No. 5,824,569, which was acontinuation-in-part of application Ser. No. 08/225,196, filed Apr. 8,1994, now U.S. Pat. No. 5,496,775, which was a continuation ofapplication Ser. No. 07/914,275, filed Jul. 15, 1992, now abandoned.

FIELD OF THE INVENTION

This invention relates to the field of integrated circuits and moreparticularly to a method for fabricating and packaging an integratedcircuit device.

BACKGROUND OF THE INVENTION

Historically, integrated circuits (ICs) have comprised a semiconductordie supported by a conductive lead frame. As illustrated in FIG. 1, thetypical IC 10 has lead frame leads 12, a die paddle 14, a semiconductordie 16 having a front side with circuitry and a back side, bond wires18, and encapsulation material or other packaging layer 20. Bond wires18 attach to bond pads (not shown) on the front of the die 16. Bondwires provide the connection between the die and the lead frame leads.The leads are attached to printed circuit boards (PCBs) or other devices(not shown).

The semiconductor industry pursues cost effective and reliable methodsto decrease the size of semiconductor packages. The development of thedual in-line package (DIP) has been instrumental in the development ofthin small outline packages (TSOPs), tape automated bonding (TAB), andchip-on-board (COB) technologies.

COB assembly processes typically include the steps of bonding a die to asubstrate and interconnecting the die to the substrate, using eitherconventional wire bond or TAB methods.

In reference to FIG. 1, TAB technology has eliminated the lead frameleads 12 and paddle 14, and instead uses TAB tape. TAB tapes comprise apredesigned network of electrical lines and buses which are attached toan IC die. The use of TAB tape and the elimination of lead frames saveon fabrication steps and costs. Typically, the die is connected to theTAB tape by a thermocompression or thermosonic bonder.

The prior processes have various disadvantages. Specifically, thetesting of IC chips occurs after the TAB tape is attached to a number ofdie and to the substrate. Thus, when reliability testing takes place,any defective die requires replacement which increases costs.Additionally, by using these processes, several steps occur while thedie is unprotected or not encapsulated which can result in additionaldie defects from increased exposure to the environment.

A semiconductor device and method for forming the device which reducesthe problems described above would be desirable.

SUMMARY OF THE INVENTION

One skilled in the art will appreciate the advantage of the subject ICand fabrication method for attaching an encapsulated and tested IC dieto a PC board. Specifically, a semiconductor packaging technique isdisclosed which is cost effective, reliable, and allows for testing ofan IC die before it is mounted to TAB tape or soldered to a PC board.Uniquely, several layers of bonded beads are formed and stacked higherthan a total IC covering.

Features of the present invention will become apparent from thefollowing detailed description of the illustrated embodiments taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE INVENTION

FIG. 1 is a cross section depicting a dual in-line package (DIP)semiconductor device.

FIGS. 2 through 5 are cross sections illustrating process steps usedwith the inventive process.

FIG. 6 illustrates the bonding of ball bonded IC die to an electricalsubstrate providing electrical connection to other devices.

FIGS. 7-8 depict cross sections of an embodiment comprising wires forconnection to bond pads.

FIG. 9 is a cross section showing the wires of FIG. 7 which have beenflamed back (heated) to form raised contacts.

FIGS. 10-13 show embodiments having channels within a wafer section.

It is noted that the illustrated embodiments are not drawn to scale, andthey are only generally representative of the features of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following U.S. patent is herein incorporated by reference: U.S. Pat.no. 4,899,107 is a discrete die burn-in for unpackaged die having sameassignee as the present invention.

The following materials are incorporated by reference herein: TapeAutomated Bonding Standardization and Implementation Requirements(Proposal), July, 1983, from the Solid State Products EngineeringCouncil, 2001 Eye Street, NW, Washington D.C. 20006. Shindo TAB, a salesbrochure for TAB tape, Toray Marketing & Sales (America), Inc., 1875South Grant St., Suite 720, San Mateo, Calif. 94402.

FIG. 2 is a detailed illustration of a first fabrication process of theinvention, and includes the following elements: IC die 30, and gold balltowers 32. Discrete conductive elements other than the conductive ballsshown are possible, such as conductive blocks or the wires as laterdescribed.

In this first process there are two steps. First, a completed IC die ismanufactured and second, gold balls are welded in a tower fashion ontoeach bond pad of the die. The balls may be formed by other means fromother materials such as solder wire or other conductive materials.

One skilled in the art will recognize that there are many methods ofcreating a tower of gold material welding beads or balls. Moreover, 5mil (1 mil=0.001 inches) wire is widely available which, after welding,will result in a ball having a diameter of about 15 mil. During thewelding process the ball will decrease in height to about 1/2 to 2/3 ofthe diameter. It is noted that any size of gold bond wire may be used tocomply with design constraints, and thus other sized balls may besimilarly manufactured. Towers may be placed on any side of the die oron several sides of the die. Additionally, the gold material suggestedmay vary to other applicable materials or percentage of materials knownfor IC welding purposes. Finally, the height of the tower will varydepending upon the size of each ball and the number of balls used in thetower, for example up to 20 mils or higher. In this embodiment, it isdesirable that the tower be higher than the encapsulating material.

The second main fabrication process is illustrated in FIG. 3. As shownin FIG. 3, the gold ball tower bonded die is placed into a cavity of acavity bar holder or other holder 34 and onto a first layer ofencapsulation material 36A.

One skilled in the art will recognize that the gold towers are exposedand facing upwards. Moreover, the encapsulating material functions as acushion between the die and holder 34, thus reducing damage. Theencapsulating material may have any desired thickness on the faces ofthe die except, in this embodiment, for the side having the towers. Thethickness of the encapsulating material on the tower side of the die isless than the height of the towers and allows for subsequent weldingsteps. Additionally, most any commonly known encapsulant material willsuffice, such as siloxane polyimide etc.

A third main fabrication process is illustrated in FIG. 4. In this stepa second layer of encapsulation material 36B is applied over the towerside of the die. Thereby, the die surface is covered while the towersare partially submerged in the material. However, it is noted that aportion of the towers are not submerged in the material. The encapsulantfills a volume not occupied by encapsulation material 36A resulting inan encapsulated IC die as illustrated in FIG. 5 after the encapsulateddevice 40 is removed from the holder 34.

One skilled in the IC fabrication art will recognize that towers 32function as leads. Therefore, the IC 40 can be tested for reliabilityand other factors before being mounted to TAB tape or a PC board 50 asillustrated in FIG. 6. Additionally, IC contamination at later steps isreduced since the encapsulating process is completed.

One skilled in the art will recognize that there are many variations tothe illustrated embodiment. The ball bonded material may be any suitablewelding material, such as compositions comprising aluminum, palladium,or other suitable materials.

The encapsulation can comprise many types of known materials suitablefor that purpose, such as siloxane polyimide and epoxy novolac basedmaterials.

There are several methods of attaching the completed ball bonded dieonto a substrate. It is possible to weld the ball tower to thesubstrate. The ball bonded die can also be clipped into a type ofreceptacle or socket, thus enabling easier removal for fasterreplacement of parts.

FIGS. 7 and 8 are cross sections showing another embodiment of theinvention. In this inventive method for forming a semiconductor device,and the structure which results therefrom, a semiconductor die 30 isprovided which has a plurality of bond pads (not shown) thereon with awire 70 such as a ball bond formed from bond wire and electricallycoupled with each pad. The die is placed in a cavity bar holder 34 orother holder. In this embodiment, no first layer of encapsulation isplaced in the holder, although a first layer to cover the bottom of theholder can be formed as with previous embodiments to completelyencapsulate the die 30. The wire comprises a protruding portion 72 whichprotrudes from the encapsulation material 36 as shown. In an alternateembodiment, a vacuum can be placed on a hole 74 through the holder 34which secures the die to the holder. An embodiment using the vacuum holemay reduce movement of the die as the encapsulation is being formed inthe cavity.

After the die is placed within the cavity of the holder, a layer ofencapsulation 36 is formed within the cavity to cover the die 30 and aportion of the bond wire 70. Either before or after the die has beenremoved from the cavity, at least a portion, or preferably all of theprotruding portion of each bond wire is removed such that the bond wireis exposed at the surface of the encapsulated device. Contact can thenbe made to some or all of the exposed portions of the bond wires.

FIG. 9 shows another embodiment of the invention. In this embodiment,the structure of FIG. 7 is formed as described above, and the protrudingportions are trimmed (if necessary) and heated. The heat exposure meltsat least a portion of the exposed protruding bond wire and results in araised contact or bump 90 which forms proximate the layer ofencapsulation as shown. Contact can then be made to some or all of theraised contacts.

In the embodiments of FIGS. 7-9 the back of the semiconductor die isexposed. Leaving the back of the die exposed may simplify themanufacturing process as forming two layers of encapsulation (one beforeplacing the die in the cavity and one after) may be eliminated. Leavingthe back of the die exposed would create no difficulties in many uses ofthe invention as the comer near the bond pads is covered byencapsulation. Also, a holder having sloped walls may aid in the removalof the encapsulated device. For example, a slope of about 10° or lesswould assist in the device removal while not excessively altering theoutline of the package.

FIGS. 10-12 show another inventive embodiment of the invention. In thisembodiment, conductive balls 100 such as those described in FIGS. 2-6are shown with one or more ball on each bond pad, although an embodimenthaving the wires as described with FIGS. 7-9 would also be sufficient.In the embodiment of FIGS. 10-12 a wafer section 102 such as a part of awafer or an entire wafer is provided which comprises a plurality ofsemiconductor die 104 with a channel 106 formed between the die 104. Thechannels can be formed chemically by etching the die, mechanically suchas by abrasive dicing, or by any workable means. The wafer section isplaced in the holder 108, then encapsulation 110 is formed within thecavity and over the wafer section and conductive balls. The conductiveballs can be completely covered as shown, or the encapsulation can beformed to cover the wafer section and leave a portion of the conductiveballs exposed. If the conductive balls are completely covered, they areexposed by removing a portion of the encapsulation such as shown in FIG.11. The encapsulation can be removed by laser ablation, chemical ormechanical means, or by other workable means. The entire surface can beplanarized or a local removal of the encapsulation proximate the bondpads is also possible. Embodiments are also feasible wherein theencapsulation is not removed and contact is made to the conductive ballsby a conductive probe which pierces the encapsulation.

After forming the encapsulation within the cavity and the channels, thedie are segmented at the channels to result in the individual diepackages 112 as shown in FIG. 12. The die can be segmented at thechannels by mechanically or chemically abrading the encapsulation whichsurrounds the die and the semiconductor material which forms the die. Inone exemplary preferred embodiment, the die are segmented using a sawblade of thickness less than the channel widths so as to leaveencapsulation material for protecting the upper peripheral edges of thedie.

FIG. 13 shows an embodiment similar to the embodiment of FIGS. 10-12wherein a plurality of conductive balls 130 are formed on each bond padand the encapsulation leaves at least a portion of one ball exposed.Removal of encapsulation to expose the ball is not required with thisembodiment.

A semiconductor device formed in accordance with the invention couldconceivably be attached along with other devices to a printed circuitboard, for example to a computer motherboard or as a part of a memorymodule used in a personal computer, a minicomputer, or a mainframe. Anassembly similar to that described in U.S. Pat. No. 5,360,992 to Lowrey,et al. which is assigned to Micron Technology, Inc. and incorporatedherein by reference, is also feasible with the inventive structuredescribed herein. The inventive device is useful in electronic devicesrelated to telecommunications, the automobile industry, semiconductortest and manufacturing equipment, consumer electronics, or virtually anypiece of consumer or industrial electronic equipment.

While the invention has been taught with specific reference to oneembodiment, one skilled in the art will recognize that changes can bemade in form and detail without departing from the spirit and the scopeof the invention. For example, instead of gravity leveling theencapsulation it may be possible to spin coat the die (or wafer or wafersection) with encapsulation to optimize the thickness of theencapsulation.

What is claimed is:
 1. An in-process semiconductor device assembly comprising:a semiconductor die having a plurality of pads thereon with at least one discrete conductive element on at least one of said pads; a holder having a cavity therein with said die removably positioned in said cavity; a layer of encapsulation material within said cavity covering said die.
 2. The assembly of claim 1, wherein a plurality of discrete conductive elements are formed over at least one of said pads.
 3. The assembly of claim 1 wherein said discrete conductive element is completely covered with said encapsulation.
 4. The assembly of claim 1 wherein said die rests on said holder.
 5. The assembly of claim 1 wherein said layer of encapsulation is a second layer of encapsulation, further comprising a first layer of encapsulation within said cavity interposed between said die and said holder.
 6. A semiconductor device assembly, comprising:a wafer section comprising a plurality of semiconductor die each having a plurality of pads thereon, with at least one conductive ball on at least one of said pads of each of said die; a holder having a cavity therein, wherein said wafer section removably lies in said cavity and contacts said holder; a layer of encapsulation material within said cavity covering said wafer section.
 7. The device of claim 6 wherein said wafer section is a semiconductor wafer.
 8. The device of claim 6 wherein said conductive balls are completely covered with said encapsulation.
 9. The device of claim 6 further comprising:a channel between said die adapted to allow separation of said die having said channel therebetween; an encapsulation material within said channel.
 10. A semiconductor device assembly comprising:a semiconductor die having a plurality of pads thereon with at least one bond wire electrically coupled with one of said pads; a holder having a cavity therein wherein said semiconductor die removably resides in said cavity and contacts said holder; a layer of encapsulation material within said cavity covering said die.
 11. The device of claim 10 wherein said bond wire comprises a protruding portion which protrudes from said encapsulation material.
 12. The device of claim 10 wherein said bond wire comprises a protruding portion which protrudes from said encapsulation material so as to form a raised contact proximate said layer of encapsulation.
 13. The device of claim 10 wherein said die is one of a plurality of unsegmented semiconductor die each having a plurality of bond pads thereon, said plurality of die forming a wafer section, further comprising at least one bond wire electrically coupled with one of said pads of each of said die.
 14. The device of claim 13 further comprising:a channel between said die adapted to allow separation of said die having said channel therebetween; and encapsulation material within said channel.
 15. The device of claim 14 wherein said each said bond wire comprises a protruding portion which protrudes from said encapsulation material.
 16. The device of claim 14 wherein each said bond wire comprises a protruding portion which protrudes from said encapsulation material such that said protruding portion forms a raised contact proximate said layer of encapsulation.
 17. A semiconductor device assembly, comprising:a wafer section comprising a plurality of semiconductor die each having a plurality of pads thereon, with at least one conductive ball on at least one of said pads of each of said die; a holder having a cavity therein, wherein said wafer section removably lies in said cavity; a first layer of encapsulation material interposed between said wafer section and said holder; and a second layer of encapsulation material within said cavity covering said wafer section.
 18. The device of claim 17 wherein said wafer section is a semiconductor wafer.
 19. The device of claim 17 wherein said conductive balls are completely covered with said encapsulation.
 20. The device of claim 17 further comprising:a channel between said die adapted to allow separation of said die having said channel therebetween; and an encapsulation material within said channel.
 21. A semiconductor device assembly comprising:a semiconductor die having a plurality of pads thereon with at least one bond wire electrically coupled with one of said pads; a holder having a cavity therein wherein said semiconductor die removably resides in said cavity; a first layer of encapsulation material interposed between said die and said holder; and a second layer of encapsulation material within said cavity covering said die.
 22. The device of claim 21 wherein said bond wire comprises a protruding portion which protrudes from said encapsulation material.
 23. The device of claim 21 wherein said bond wire comprises a protruding portion which protrudes from said encapsulation material so as to form a raised contact proximate said layer of encapsulation.
 24. The device of claim 21 wherein said die is one of a plurality of unsegmented semiconductor die each having a plurality of bond pads thereon, said plurality of die forming a wafer section, further comprising at least one bond wire electrically coupled with one of said pads of each of said die.
 25. The device of claim 24 further comprising:a channel between said die adapted to allow separation of said die having said channel therebetween; and encapsulation material within said channel.
 26. The device of claim 25 wherein said each said bond wire comprises a protruding portion which protrudes from said encapsulation material.
 27. The device of claim 25 wherein each said bond wire comprises a protruding portion which protrudes from said encapsulation material such that said protruding portion forms a raised contact proximate said layer of encapsulation. 